1. Technical Field
This invention relates to a rotation detector and to a method of producing a rotor in the rotation detector.
2. Description of the Related Art
A rotation detector for detecting the angle of rotation of a rotary member by utilizing magnetism is known as a magnetic encoder. The rotation detector includes a part that is periodically indented, such as a gear.
FIG. 9 is an exploded perspective view of a rotor in a rotation detector according to a prior art. As shown in FIG. 9, the conventional rotation detector includes a gear 100 for detecting position signals to detect the rotational position and the speed of rotation, and a ring 200 for detecting a signal of one rotation to detect the position of origin in one rotation. These gear 100 and ring 200 are overlapped concentrically to constitute a rotor. In the prior art, in order to attach the gear 100 and the ring 200 concentrically to each other thereby maintaining high precision, the gear 100 and the ring 200 must be precisely machined.
Therefore, according to Japanese Patent No. 4085074, a single gear is formed and, thereafter, a single groove is formed in the gear in the circumferential direction to separate it into an upper part and a lower part. Then, for example, the upper part is ground leaving only one tooth.
Japanese Unexamined Patent Publication No. 4-335111 proposes a method of forming, as a unitary structure, a gear 100 for detecting position signals and a single tooth on a ring for detecting a signal of one rotation by forming and sintering a magnetic material.
However, according to Japanese Patent No. 4085074, the teeth are once all formed even on the upper part and are, thereafter, all ground leaving one tooth accompanied, therefore, resulting in very low working efficiency.
Japanese Unexamined Patent Publication No. 4-335111 can be applied only to a case where the rotor can be produced by using a material that can be sintered. Therefore, when it is attempted to produce a rotor by using steel to attain higher strength, the method disclosed by Japanese Unexamined Patent Publication No. 4-335111 cannot be applied.
The present invention was accomplished in view of the above circumstances and has an object of providing a rotation detector including a rotor that can be efficiently produced by machining.